The following is a report on the development of two unique and separate
cofferdam systems used in the construction of the marine foundations for the I-
205 Columbia River Bridge at Portland, Oregon for the Oregon Department of
Transportation. The first of these two systems utilized interlocking H-pile 100 ft
long to form a cofferdam 145 ft by 58 ft in plan and 100 ft deep. The second
system consisted of two immense bell shaped steel forms. The larger of the two
forms was 83 ft by 66 ft in plan, 62 ft high and weighed 450 tons. This form was
externally stiffened for a designed hydrostatic head of 54 ft. Both forms were
designed, except for the top 14 ft, to be set and stripped in one solidly welded
unit. The supporting geological formation for the bridge foundations is the
Troutdale, a cemented sand and gravel. This formation is at the ground surface
on the Washington Shore and slopes downward to a depth of 115 ft below
normal high water at about mid-channel. In this area the Troutdale formation is
covered with a layer of fine to medium sand 90 to 100 ft thick. It was the variable
depth of the Troutdale which determined the two types of foundations and the
corresponding to the two cofferdam systems.
Author: Robert B. Bittner, Ben C. Gerwick, Inc.
Publisher: DFI